The present invention relates to novel and improved apparatus for removing contaminants from liquids, typically those used as coolants and lubricants in machining operations, or the like. More specific features of the invention, in the context of a liquid filtration system, relate to means for adjustably establishing the vertical angle of travel of a movable filter media to improve filtering efficiency, and to improved means for preventing unfiltered liquid from mixing with filtered liquid.
Among the filtration systems commonly used to remove solid contaminants from liquids for recycling in machine tool operations are those wherein an endless chain or belt is moved through a tank to which contaminated liquid is supplied. A layer of liquid-pervious media is carried on the upper surface of the chain, fresh media being supplied from a roll supported at the rear end of the tank and used media discharged at the front end. The media travels downwardly to some extent from the rear end as it enters the tank, and thence upwardly to the front end. Dirty liquid is contained in a pool on the upper surface of the media between the tank side walls or other side structure and sealing means are provided to prevent escape of dirty liquid at the lateral edges of the media. Contaminants are deposited on the surface of the media as it travels through the tank, the clean liquid which passes through the media being collected in the lower part of the tank and pumped back to the location of the machining operation.
Contaminants form a bed or "cake" as they collect on the surface of the media. As the thickness of the cake increases, filtering efficiency is enhanced by retaining smaller particles on the cake itself. However, the flow rate through the media decreases proportionately to the increase in cake thickness if the pressure differential between the dirty and clean liquid compartments remains constant. Thus, it is desirable to maintain the head of dirty liquid as high as possible, particularly in so-called gravity filters which do not include means for creating a vacuum (i.e, a pressure below atmospheric) in the clean liquid compartment. Since the upper level of the dirty liquid pool cannot exceed the lowest height of the seals along the lateral edges of the pool, it is apparent that a deeper pool of dirty liquid may be maintained by providing the highest practical level of edge sealing.
In typical forms of so-called flat bed filtration apparatus, as seen, for example, in U.S. Pat. Nos. 3,704,787, 3,876,547 and 4,137,169, a seal to prevent dirty liquid from leaking past the lateral edges of the media into the clean liquid below is provided by cooperative structure affixed to the tank wall and to the movable chain and/or media. In U.S. Pat. No. 4,220,539 the media is wider than the chain and outer portions of both the media and the chain rest upon shelves extending inwardly from opposite side walls of the tank to form a plurality of transversely spaced dams providing a labyrinthine leakage path in combination with leakage collecting inclined troughs on each side draining into a contaminated liquid chamber. While such edge sealing and leakage collecting troughs are effective for use in flat bed filtration systems, they would not be suitable for use in apparatus wherein the edge seals are provided by contact between moving media and rotating guide wheels. In another prior art type of filtration apparatus, with which the present invention is principally concerned, edge seals are provided by direct contact of the media upper surface with lower peripheral portions of guide wheels under which the media and upper run of its supporting chain pass. Thus, the height of the edge seals, and corresponding maximum depth of the dirty liquid pool, is greatest when the media contacts the guide wheels over the largest possible portion (i.e., approaching 180.degree.) of their lower peripheries. This means, of course, that the vertical angle of travel of the media as it exits the pool of dirty liquid approaches 90.degree.. However, when the cake builds up rather rapidly it may fall off the surface of a steeply inclined media back into the dirty liquid pool rather than exiting the tank with the used media. While a certain amount of cake build-up is desirable for reasons previously explained, the rate of liquid flow is unacceptably slow when the amount of contaminants in the dirty liquid compartment becomes too great. Furthermore, although the operation is normally controlled to ensure that the height of the dirty liquid pool does not exceed that of media-guide wheel engagement, some dirty liquid occasionally spills around the sides and some may also leak through the normally sealed engagement of the media surface and peripheries of the guide wheel.
It is an object of the present invention is to provide liquid filtration apparatus wherein the depth of the dirty liquid pool may be selectively controlled, consistent with the requirement for contaminant removal via a filter media interposed between dirty and clean liquid compartments. More specifically, this object of the invention is concerned with providing means for readily adjusting the angle or slope of a continuous, traveling web of filter media as it exits a pool of dirty liquid in filtration apparatus.
An additional object of the invention is to provide, in filtration apparatus wherein edge sealing is accomplished through contact of the media upper surface with a pair of guide wheels at each side of the dirty liquid pool, improved means for preventing liquid which escapes from the dirty liquid pool from mixing with the clean filtrate.
Other objects will in part be obvious and will in part appear hereinafter.